title: Regulation of the activity of chloroplast translational initiation factor 3 by NH2- and COOH-terminal extensions.
abstract: The mature form of the chloroplast translational initiation factor 3 (IF3chl) from Euglena gracilis consists of an internal region homologous to prokaryotic IF3 flanked by long NH2- and COOH-terminal extensions. Sequences in these extensions reduce the activity of the homology domain in promoting initiation complex formation with chloroplast mRNAs and 30 S ribosomal subunits. A series of deletions of the NH2- and COOH-terminal extensions of IF3chl were constructed and tested for their effects on the activity of the homology domain. About half of the inhibitory effect arises from sequences within 9 residues of the junction between the NH2-terminal extension and the homology domain. The remaining inhibitory effect is the result of sequences in the COOH-terminal extension. The equilibrium constant governing the binding of the homology domain of IF3chl to 30 S subunits is estimated to be 1.3 x 10(7) M-1. Sequences close to the junction of the NH2-terminal extension and the homology domain reduce this binding constant about 10-fold. Sequences in the COOH-terminal extension have a similar negative effect. The negative effects of these two regions are cumulative, resulting in a 100-fold reduction of the binding constant. The 9 residues at the NH2-terminal extension effectively prevent the proofreading activity of IF3chl. The entire COOH-terminal extension reduces the proofreading ability by about half. These results are discussed in terms of the proposed three-dimensional structure of the homology domain of IF3chl.
authors.affiliation: Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599-3290, USA.
authors.forename: N J
authors.initials: NJ
authors.lastname: Yu
authors.forename: L L
authors.initials: LL
authors.lastname: Spremulli
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism*; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000737:chemistry; D005056:Euglena gracilis / Q000378:metabolism*; D008958:Models, Molecular; D010446:Peptide Fragments / Q000235:genetics / Q000494:pharmacology; D010448:Peptide Initiation Factors / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D039881:Prokaryotic Initiation Factor-2; D039665:Prokaryotic Initiation Factor-3; D011485:Protein Binding; D014176:Protein Biosynthesis / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics; D012270:Ribosomes / Q000737:chemistry / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D010446:Peptide Fragments; D010448:Peptide Initiation Factors; D039881:Prokaryotic Initiation Factor-2; D039665:Prokaryotic Initiation Factor-3; D012333:RNA, Messenger; D016601:RNA-Binding Proteins